You don't seem to understand.
Nobody puts black tape on the top of their visor, that's ridiculous.
I was making a point that the peak is essentially part of the helmet. Functionally, it makes the eye port smaller. You can do the same thing by putting a piece of cardboard inside the helmet behind the visor to make the eye port smaller. Which again, is ridiculous. Nobody does that.
If you want to block more sun without a peak, tilt your head a bit lower.
As for roost, it depends on the helmet and the length of the peak, but most ADV helmets have shorter peaks than MX helmets, so you have to tilt your head lower to block roost.
This is the peak of a typical MX helmet:
This is the peak on the Arai XD-4 your friends were talking about:
How far down do you have to tilt your head to block roost coming from the bike's rear tire in front of you?
MX helmets were never designed to block the sign. That's not their purpose. They're long enough to block roost because most MX bikes don't have a windshield and the attack position on a dirt bike is head over the handlebars.
Some ADV helmets have peaks long enough to block roost. Most aren't.